Frequency control distribution



April 7, 1936..

H. A. AJFIFEIL. 2,,fi, FREQUENCY CONTROL DISTRIBUTION Filed Aug. 29,1934 2 Sheets-Sheet l Primary J'z'arzdard aw G y Secondary ATTORNEY in 9m.

H. A. AFFIEL FREQUENCY CONTROL DISTRIBUTION Filed Aug. 29, 1934 v 2Sheets-Sheet 2 .59 con dary Standard INVENTOR ATTORNEY Patented Apr. 7,1936 UNITED STATES FATENT QFFEQE FREQUENCY CONTROL DISTRIBUTIONApplication August 29, 1934, Serial No. 741,980

13 Claims.

This invention relates to frequency control distribution, and itspurpose is to insure adequate reliability in the transmittal of standardfrequencies over lines and their use for the synchronizing of radiostations, or for other purposes.

In present day communication it is becoming increasingly important tohave available at certain places an alternating current of a veryprecise and constant frequency which may be used directly forcommunication or which may be used as the control for frequencychangers, such as harmonic generators, from which may be obtained otherparticular frequencies desired.

One field of use of such standard frequencies is in connection withbroadcasting a program from a plurality of radio stations which are tobe operated in synchronism. Other important uses are in connection withnumerous applications in telephony and in telegraphy and in comparisonor standardization of timepieces.

The difficulty of maintaining a standard source of frequency of therequisite precision and stability is sufficiently great so that it isadvantageous to have one such master source maintained as a primarysource from which its frequency or related frequencies may betransmitted to numerous outlying stations. Occasionally secondarystandards may be advantageously located at a few outlying points, thesesecondary standards being normally controlled by the frequency from theprimary source and serving in turn smaller areas if called upon to doso. Having received the standard frequency at any station, the actualdesired frequency may then be obtained in any desired manner such, forexample, as that disclosed in patent to Marrison No.

1,931,873, October 24, 1933, or in application of Gannett, Serial No.739,989, filed August 15, 1934.

In this invention, the purpose is to so relate a primary source withoutlying stations and with secondary sources located at appropriatepoints as to insure, by suitablewire networks, the greatest reliabilityof service possible. The invention will be better understood byreference to the following specification and accompanying drawings,

in which Figure 1 illustrates by conventionalized circuits theapplication of my invention to three outlying stations; Fig. 2 shows thesame arrangement in somewhat greater detail; Fig. 3 shows theapplication of the invention to four points trates one manner ofassociating the secondary standard to the system; Figs. 7 and 7a givedetails of the connections for any one point of such a circuit as thatof Fig. 6; and Figs. 8, 9 and 10 illustrate alternative means forpreventing undesirable cross-connections between various circuits.

It will be appreciated that a complete frequency distribution networkhas increased reliability to the extent that there are many substandardsprovided and also to the degree with which emergency or alternativeroutes are included in the line circuits. The latter feature isillustrated, for example, in Fig. 1, in which it is the desire todistribute a standard frequency from a point 0 to three stations, A, Band C, which are here shown as radio stations. A desirable line systemwould include not only lines radiating from O to A, B and C,respectively, but also cross-connections such as AB and B-C, so that inthe case of failure of such a line as OA, radio station A would stillreceive its frequency over route OB-A. Even though two of the lines suchas OA and OB are interrupted, all three stations would still receivefrequency over the circuit OCBA.

For the distribution of standard frequencies in certain districts wherethe line circuit will ordinarily be non-loaded cable pairs, such apermanently connected network as illustrated in Fig. 1 could be readilyprovided. With stations further apart, however, amplification wouldfrequently be required in the wire connecting circuits. Such a system isshown in Fig. 2, in which amplifiers are shown in a conventionalizedmanner by a triangle, the amplifiers being unilateral in action and thedirection of transmission being indicated by the apex of the triangle.Thus, in Fig. 2, the lines radiating from the primary source A includeone-way repeaters. However, in the case of the cross-connectingemergency links, transmission would ordinarily be required in eitherdirection on the occasion of a break in the circuit. For this reason theamplifiers in the cross-connecti ng lines should be two-way in theiroperation and might Well consist of the 2l-type repeater or the 22-typerepeater, both of which are now well known to those acquainted with theart of communication, and these repeaters are shown in highlyconventionalized form in Fig. 2. In some cases it would be desirable touse complete four-wire circuits in the cross-connecting emergency links,as shown in Fig. 3.

This Fig. 3 incidentally shows four radio stations, and illustrates thesituation where many radio stations are located at important citiesthroughout the country and in which there are radiating wire circuitsfrom the central source and there are provided also cross-connectionemergency circuits. It should be pointed out, however, that in settingup such a network certain difliculties arise. For example, with thegeneral use of repeaters or amplifiers, there would be a natural desireto make the gain over these circuits as large as feasible, and therewould result the danger of singing being set up, particularly in theloop combinations of the twoway circuits between any two stations. Also,there would be phase difficulties where the power is received at a pointfrom several sources or over several routes. Then, again, in anextensive system, the points will be sufficiently remote and the numberof stations frequently great so as to justify the employment ofsecondary standards at various points in order to insure continuance ofservice in case of complete failure of the primary standard or the linesradiating directly therefrom.

One way of meeting these difficulties is illustrated in the circuit ofFig. 4 which, among other things, shows the general use of four-wirecircuits interconnecting all the points involved, and also shows theemployment of at least one secondary standard which will be available atall times for service and is synchronized with the primary standard, atthe same time continuing to supply approximately correct frequency ifthe primary standard source is removed. In this figure there is shown aprimary standard at a point 0 from which the desired frequency currentis to be supplied to radio stations A, B and C. The two directionalpaths of each four-wire circuit interconnecting the radio stations willindependently form what may be termed the primary and secondarynetworks, indicated by the letters (P) at (S), is respectively. Eachradio station will be fed its frequency simultaneously from the twonetworks through balancing devices or one-way amplifiers, asillustrated, which will effectively prevent current from one networkreaching the other except through the secondary standard shown aslocated at the station B, and which it is understood is to be controlledfrom the primary network. This means that each secondary standard isavailable not only to feed the radio station in the immediate vicinityof this standard itself, but also to serve as a source of standardfrequency for the network as a whole, even though the primary standardwere completely isolated by failure of all of the interconnecting wires.

This secondary standard would be of any suitable form, preferably quitesimilar to the primary standard, and might very well take on the form ofthe so-called crystal-control oscillator. In any event, it would be sodesigned that it is kept in step with the input frequency from theprimary, but if the latter is interrupted, then it will continue togenerate independently a constant frequency. A suitable connection forthis purpose is illustrated in Fig. 5, in which the secondary source isintroduced into a 21-type circuit where it is available to receivecontrolling frequency from the primary and is available also to feed outfrequency in either direction, as indicated in Fig. 5.

{I'he general arrangement of Fig. 4 is shown more extensively applied inFig. 6 in which nine points instead of three are involved. In this caseeach radio or other station is served by at least three general sourcesof frequency, transmitting in both directions. For the middle station H,for example, six sources are involved, and it will be apparent that acomplete failure of the frequency supplied to this station would requirefailure of an extremely large number of pairs of wires in the system asa whole.

The method of connection to the take-off points is shown in Fig. '7 forthe station K, and the exact connections for this station are shown ingreater detail in Fig. 7a which is drawn to indicate completely the twowires comprising a pair instead of a single line, as has been used inthe conventionalized circuits of the previous figures. The boxes Pindicate phase controllers for the purpose of properly relating thephases of the frequency supplied over the different circuits. Amplifiersare used partly for the purpose of controlling the magnitude of theimpulses over any one line, but still more because of the unilateralcharacteristics of these amplifiers which insure that there is no directcrossconnection between the primary (P) and secondary (S) supplycircuits which might otherwise introduce singing difficulties in thenetwork as a whole.

The matter of avoiding such singing conditions is of prime importanceand may be brought about in a number of different ways. One is thatillustrated in Fig. 7a, in which unilateral amplifiers are used, asalready indicated. A second method would be that shown in Fig. 8, whichmakes use of a hybrid coil arrangement which electrically separates the(P) and the (S) circuits. that shown in Fig. 9, where an amplifier relayarrangement controlled by oscillations coming over the (P) circuitnormally maintains the transmission to the radio station from theprimary source, but on failure of this source the relay automaticallyswitches the connections to the secondary source. This arrangement hasthe advantage that it avoids the phase difiiculties which mightotherwise arise if the radio transmitters or other synchronizing devicesreceived current continuously from two or more sources.

Still a further alternative is shown in Fig. 10, in which case it isdesired to insure that the frequency supplied from two sourcessimultaneously will combine in phase favorably and not result in abalancing out of the currents received from two sources. This figureshows an amplifier relay arrangement II which normally keeps a circuit12 open, but on failure of the frequency to appear in suflicientamplitude, the relay M closes a contact for circuit I2 and starts alow-period pendulum I3 into oscillation, thus alternately reversing thepolarity of the incoming frequency over the (S) circuit. If the lowamplitude of the standard frequency arriving at I I resulted from thedephasing of the two incoming sources, then a 180 shift in the oneincoming source would cause the two sources to add rather than subtract,at which time the relay M opens the circuit l2 and the periodicalreversals cease. This device has the added advantage that in the eventof the complete failure of both sources, the continued periodic actionof the reversing device would act as an alarm.

The invention has been described in a very general way, and it is to beunderstood that many variations and modifications may be introducedwithout departing from the spirit of the invention.

What is claimed is:

1. In a frequency control distribution system, a.

Still another arrangement would be source of standard frequency and aplurality of stations to be supplied with the standard frequency, themethod of maintaining the supply of standard frequency to each stationwhich consists in transmitting standard frequency to each stationseparately and in relaying this frequency both ways between each stationand each of the other stations whereby each station may receive standardfrequency over a plurality of paths.

2. The combination of claim 1 characterized by the fact that the phaseof arrival of the current over each path is adjusted so that allcomponents come together in substantially the same phase.

3. In a frequency control distribution system, a source of standardfrequency, a plurality of sta- 'tions, transmission lines from thesource to each station for transmitting standard frequency current,means for relaying the received current from each station to each otherstation, and means for bringing the frequency currents from the variousdirections into phase.

4. In a frequency control distribution system, a source of standardfrequency and a plurality of stations, transmission lines from thesource to some of the plurality of stations, and a plurality of oppositetwo-way cross-connections between the stations whereby each stationreceives frequency current from a plurality of directions.

5. In a frequency control distribution system, a source of standardfrequency and a plurality of stations, transmission lines from thesource to some of the plurality of stations, a plurality ofcross-connections between the stations whereby each station receivesfrequency current from a plurality of directions, and means at eachstation for bringing the frequency currents from the various directionsinto phase.

6. In a frequency control distribution system, a source of standardfrequency and a plurality of stations, transmission lines from thesource to some of the plurality of stations, and connections from eachstation to each of a plurality of the stations, each connectionconsisting of two unilateral oppositely directed connections wherebyeach station receives and sends out frequency current over independentpaths to each of a plurality of stations.

7 In a frequency control distribution system, a source of standardfrequency and a plurality of stations, transmission lines from thesource to some of the plurality of stations, and fourwire circuitconnections from each station to each of a plurality of the stationswhereby each station receives and sends out frequency current overindependent paths to each of a plurality of stations.

8. The combination of claim 6 characterized by the fact that certain ofthe incoming circuit connections to a station have phase shiftingdevices to bring the resultant incoming current to a station to adesired value and phase.

9. In combination, a plurality of transmitting stations, two sources ofstandard frequency A and B, connections therefrom to said transmittingstations, further connections between the said transmitting stations,all those connections forming a network, and means at source B to keepit adjusted to the frequency of source A as that frequency is receivedthrough the network from source A, said sources A and B each beingoperable independently of each other so that source B continues itsoperation to supply the approximate standard frequency to the networkswhenever source A ceases operation.

10. In the operation of a network of connected transmitting stationswith two independently operable sources of standard frequency A and Bconnected through the network to the transmitting stations, the methodwhich conists in supplying a standard frequency to the network byfeeding the standard frequency from each of the two standard frequencysources A and B into the network at difierent places, applying thefrequency transmitted from the source A through the network to maintainthe frequency of the source B adjusted thereto, and continuing theoperation of the source B to supply approximately that frequency of thenetwork whenever source A ceases operation.

11. In a frequency control distribution system, a source of standardfrequency and a plurality of stations, transmission lines from thesource to some of the plurality of stations and connections from eachstation to each of a plurality of stations, each connection consistingof two unilateral oppositely directed connections whereby each stationreceives and sends out primary standard frequency current overindependent paths to each of a plurality of stations, and secondarysources of standard frequency, and means whereby they serve any part ofthe system which may be cut off from the primary source.

12. In combination, a plurality of transmitting stations, a centralsource of standard frequency, connections therefrom to said transmittingstations, further connections between transmitting stations, and at eachstation phase adjusters in all the connections thereto, except one, bywhich the currents of standard frequency to each station may be adjustedto be in the same phase for each station.

13. In combination, a plurality of transmitting stations, a source ofstandard frequency, connections therefrom to said stations, and furtherfour-wire connections between stations whereby each station may get itscurrent directly from the source or indirectly by way of other stations.

HERMAN A. AFFEL.

